Methods for the reduction of bleeding of lignosulfonates from lignosulfonate-treated substrates

ABSTRACT

The bleeding of lignosulfonates from lignosulfonate-treated substrates when contacted under humid conditions is reduced by rendering the lignosulfonates water-insoluble via reacting them with an amine polymer-epichlorohydrin adduct containing at least one quaternary ammonium group under acidic conditions.

This is a division of Ser. No. 09/923,218 filed Aug. 6, 2001 now Pat.No. 6,458,419; which is a division of Ser. No. 09/466,164 filed Dec. 17,1999 now U.S. Pat. No. 6,281,350 issued Aug. 28, 2001.

FIELD OF THE INVENTION

The present invention relates to methods of reducing the bleeding oflignosulfonates from lignosulfonate-treated substrates when contactedunder humid conditions by rendering the lignosulfonates water insoluble.

BACKGROUND OF THE INVENTION

Lignosulfonates are water-soluble materials. They are used in variousapplications and products, such as preparation of concrete admixtures,feed pellets, oil drilling muds, road stabilization, emulsion anddispersion stabilization, plant nutrition, leather tanning, dustcollection, road de-icing and other applications. Lignosulfonates aremetal or ammonium salts of lignosulfonic acids, and are eitherby-products of the sulfite pulping process, or products of sulfonationof other lignin derivatives. Lignin derivatives include, but are notlimited to, kraft lignin, organosolv lignin, chemically modified ligninderivatives, and mixtures thereof.

Lignosulfonates can also be used to strengthen various substrates bytreating them (e.g. coating, impregnating, etc.) with lignosulfonatesolutions. Examples of these substrates are lignocellulosic-basedsubstrates (such as paper, cardboard, and webs containing mixtures oflignocellulosic and polymer fibers). Note that for the purposes of thisdisclosure the terms “lignocellulosic-based substrates” and “substrates”will be used interchangeably. However, one major problem with using thelignosulfonates in the strengthening applications above is that theybleed off the substrates when contacted under humid conditions (e.g.touched with wet hands). This results in poor aesthetics, increasedmessiness, and poor strength retention. One method to reduce oreliminate this bleeding is to coat the treated substrates with wax orpolymer films. However, this coating method is not an effective solutionbecause the secondary coating materials are expensive to purchase,process and apply. Yet another method to reduce or eliminate thebleeding of the water-soluble lignosulfonates is to insolubilize them bycrosslinking.

The crosslinking reactions for lignosulfonates that have been reportedin the literature include the following: 1) condensation reaction withstrong mineral acids at elevated temperatures (via the SO₃ ²⁻ units); 2)oxidative coupling reaction with hydrogen peroxide and catalysts (viathe OH⁻ groups); 3) reaction with bis-diazonium salts (via theα-position to the OH⁻ groups); 4) reaction with bifunctional acidchlorides (via the OH⁻ groups); 5) reaction with cyanuric chloride (viathe OH⁻ groups); 6) reaction with formaldehyde (via the CH₂ groups); 7)reaction with furfural (via the α-position to the OH⁻ groups); and 8)reaction with epichlorohydrin (via the OH⁻ groups). However, the abovereactions/processes include various processing problems, such as cost,low pH, long reaction times, harsh conditions (e.g. temperature), healthhazards, etc.

What have been missing are simple and inexpensive methods to renderlignosulfonates water insoluble, thus reducing or eliminating theirbleeding from the lignosulfonate-treated substrates when contacted underhumid conditions.

SUMMARY OF THE INVENTION

The present invention relates to methods of rendering lignosulfonateswater insoluble by reacting them with an amine polymer-epichlorohydrinadduct containing at least one quaternary ammonium group under acidicconditions. This results in reduction of the bleeding problem of theoriginally water-soluble lignosulfonates from the substrates whencontacted under humid conditions.

DETAILED DESCRIPTION OF THE INVENTION

It is known that the strength of lignocellulosic-based substrates (e.g.paper, linerboard, corrugated, cartonboard, etc.) can be improved bytreating them with various aqueous solutions of strengthening agents(e.g. sodium silicate, starch, carboxy methyl cellulose—CMC, xylan,etc.). Unfortunately, these water-soluble strengthening agents bleed offthe substrates when contacted under humid conditions.

Lignosulfonates are water-soluble strengthening agents that can also beused to strengthen lignocellulosic-based substrates. The lignosulfonatescontain sulfonic units (HSO₃ ⁻; also called hydrogen sulfite units) andsulfonate units (SO₃ ²⁻; also called sulfite units), and for thepurposes of this disclosure the term “sulfonic” will be used toencompass both “sulfonic” and “sulfonate” units. It is expected that thelignosulfonates strengthen the lignocellulosic-based substrates byreinforcing their fibers and/or fiber bonds, via encapsulation and/orpenetration. Lignosulfonates are examples of a variety of possiblelignin derivatives that may be used. Lignin derivatives include, but arenot limited to, kraft lignin, organosolv lignin, chemically modifiedlignin derivatives wherein the nucleophilic sulfonic unit is preserved,and mixtures thereof.

Unexpectedly it was found that an aqueous calcium lignosulfonatesolution (LIGNOSITE 50; Georgia-Pacific Inc.; Atlanta, Ga.), containing40% calcium lignosulfonate and 10% inert solids, when mixed togetherwith aqueous amine polymer-epichlorohydrin adducts containing quaternaryammonium groups under acidic conditions exhibits a virtuallyinstantaneous reaction that results in a precipitate. This precipitateexhibits water-insoluble properties. This mixing is a simple,inexpensive, and fast process that is carried out under ambientconditions and without the need for complex pieces of equipment. Atacidic pH levels, such as pH=3, amine polymer-epichlorohydrin adductscontain quaternary ammonium groups and have a charge density of about3.2 meq/g. It was also unexpectedly found that aqueous sodiumlignosulfonate (LIGNOSITE 458; Georgia-Pacific Inc.) and ammoniumlignosulfonate (LIGNOSITE 1740; Georgia-Pacific Inc.) when independentlymixed together with an aqueous amine polymer-epichlorohydrin adductcontaining quaternary ammonium groups under acidic conditions exhibit avirtually instantaneous reaction that results in a precipitate.

For the purpose of this disclosure, the term “aminepolymer-epichlorohydrin adduct(s)” refers to any resins made by thereaction of a polyamine or an amine-containing polymer with an epoxidepossessing an epichlorohydrin second functional group. Two commerciallyavailable amine polymer-epichlorohydrin adducts containing quaternaryammonium groups at pH=3 are KYMENE® 450 and KYMENE® 557H from HerculesInc. (Wilmington, Del.). These KYMENE® products contain 20% and 12.5%solids, respectively. The amine polymer-epichlohydrin is also referredto as either: a) polyamide polyamine epichlorohydrin (PAE), or b)poly(aminoamide) epichlorohydrin, or c) amino polyamide epichlorohydrin,or d) polyamide epichlorohydrin, or e) amine polymer-epichlorohydrin(APE), or f) polyalkylenepolyamine-epichlorohydrin (PAPAE). For thepurposes of this disclosure the term “KYMENE®” shall refer to the classof amine polymer-epichlorohydrin adducts, more commonly known aspolyamide polyamine epichlorohydrin resins, containing quaternaryammonium groups at pH=3. KYMENE® is a compound that is used as awet-strength agent in paper applications. Preparation of KYMENE® isdescribed in great details in Keim, U.S. Pat. No. 2,926,116, issued Feb.23, 1960; Keim, U.S. Pat. No. 3,332,901, issued Jul. 25, 1967; Keim,U.S. Pat. No. 3,700,623, issued Oct. 24, 1972; and Keim, U.S. Pat. No.4,537,657, issued Aug. 27, 1985. Although it is known that KYMENE® has astrong affinity for itself (as it crosslinks primarily with itself) anda slight affinity for cellulose or CMC (via the cellulose's carboxyl),it has never been disclosed or found that KYMENE® has a strong affinityfor lignosulfonates.

As referenced in U.S. Pat. No. 4,537,657, KYMENE® 450 aminepolymer-epichlorohydrin adduct at pH=3 has the general formula

Another commercial source of a useful polyamide polyamineepichlorohydrin compound containing quaternary ammonium groups at pH=3is Henkel Inc. (Düsseldorf, Germany), which markets such compound underthe trademark Fibrabond™, as referenced in U.S. Pat. No. 5,239,047.

Without wishing to be bound by theory, we believe that the crosslinkingtakes place between the highly nucleophilic sulfonic or sulfonate unitsof the lignosulfonate and the quaternary ammonium groups of the aminepolymer-epichlorohydrin adduct. Furthermore, we believe that 3-Dmolecular conformations, active unit spacings and charge density, andsteric effects play important roles in determining the strength of thecrosslinking association. The above hypotheses were tested in variousseries of experiments.

In the first series of experiments, various lignosulfonate solutionswere tested with KYMENE® 450 at pH=3, to determine which ones reactsimilarly to LIGNOSITE 50. Out of the 20 lignosulfonate solutionssupplied by Westvaco (Westvaco Inc., New York, N.Y.), Lignotech(Borregaard Lignotech Inc., Sarpsborg, Norway), and Georgia-Pacific only16 (Westvaco's REAX 83A, Westvaco's REAX 85A, Westvaco's KRAFTSPERSEEDF450, Lignotech's WANIN S, Lignotech's UFOXANE 3A, Lignotech's NORLIGG, Lignotech's NORLIG A, Lignotech's MARASPERSE N-22, Lignotech'sMARASPERSE N-3, Lignotech's MARASPERSE AG, Lignotech's MARASPERSE CBA-1,Lignotech's WELLTEX 200, Lignotech's WELLTEX 300, Lignotech's WELLTEX300F, Georgia-Pacific's LIGNOSITE 1740, and Georgia-Pacific's LIGNOSITE458) formed a precipitate similar to that of LIGNOSITE 50. Finally,kraft lignin (INDULIN AT from Westvaco Inc.), which has hydroxyl but notsulfonic/sulfonate units, could not form a precipitate with KYMENE® 450.Polystyrene sulfonate (from Aldrich Inc., Milwaukee, Wis.), which hassulfonic but not hydroxyl units, was combined with KYMENE® 450 andresulted in a precipitate. However, polyvinyl sulfonate (from AldrichInc.) did not form a precipitate when combined with KYMeNE® 450. All theabove experiments point to the fact that the existence of thesulfonic/sulfonate units in a compound is a necessary but not asufficient condition for a reaction between this compound and KYMENE®450 to form a precipitate.

On the other hand, the importance of the 3-D molecular conformation,active unit spacing, and steric effects of amine polymer-epichlorohydrinadducts containing quaternary ammonium groups under acidic conditionswas tested by reactingpoly(3-chloro-2-hydroxypropyl-2-methacroxyethyl-dimethylammoniumchloride) [CAS # 76123-64-3; Polysciences Inc.; Warrington, Pa.], whichis not an amine polymer-epichlorohydrin adduct but has quaternaryammonium groups and a charge density of 3.5 meq/g at pH=3, withlignosulfonate. The resulting product was a thickened slurry of the twopolymeric compounds, unlike the precipitate between lignosulfonate andKYMENE®.

In another series of experiments designed to emphasize the importance ofthe quaternary amine group of amine polymer-epichlorohydrin adducts,polyethylenimine (PEI; Aldrich Inc.) which contains tertiary amines wasmixed with lignosulfonate and produced a water-soluble thickened slurry,unlike the precipitate between lignosulfonate and KYMENE®.

It was also discovered that the precipitate between lignosulfonate andKYMENE® will only stay water-insoluble within a certain pH range. Morespecifically, it was discovered that certain alkaline conditions, whichmay be dependent upon the compounds reacted, will solubilize theprecipitate. For example, the precipitate from the reaction of calciumlignosulfonate LIGNOSITE 50 and KYMENE® 450 will solubilize in water ifthe pH is about 11 or higher.

This crosslinking reaction and treatment can be applied to the substrateat any stage of the substrate manufacturing process. If the substrate inlignocellulosic material, the stages of the manufacturing processinclude the pulp stage, wet end of the paper making process (e.g. in theheadbox, or formation section, or press section), and dry end (e.g. inthe drying section or size press), or even to dry material alreadyprocessed (e.g. linerboard, and medium) and formed into final products(e.g. corrugated board). In general, there are two methods to form theprecipitate and apply it to the substrates.

In the first method, the precipitate is formed in the substrate (alsocalled in-situ method) and in the second method the precipitate ispre-formed and then applied to the substrate. In one variation of thein-situ method, the water-soluble strengthening agent containing atleast one nucleophilic sulfonic unit is applied to the substrate firstand the amine polymer-epichlorohydrin adduct containing at least onequaternary ammonium group is applied second. In another variation of thein-situ method, the amine polymer-epichlorohydrin adduct containing atleast one quaternary ammonium group is applied to the substrate first,and the water-soluble strengthening agent containing at least onenucleophilic sulfonic unit is applied second. Various methods may beused to apply both the amine polymer-epichlorohydrin adduct containingat least one quaternary ammonium group and the water-solublestrengthening agent containing at least one nucleophilic sulfonic unit.Such methods of application include, but are not limited to, immersion,coating, and incorporation by pressure (e.g. MIPLY pressure saturationmethod; U.S. Pat. No. 4,588,616 herein incorporated by reference). Thechosen method to apply the amine polymer-epichlorohydrin adductcontaining at least one quaternary ammonium group need not be the sameas the chosen method to apply the water-soluble strengthening agentcontaining at least one nucleophilic sulfonic unit.

The in-situ method can be used for a single substrate as well as for alaminate structure of plies of substrates. In the latter case, thecompound containing the sulfonic units and the aminepolymer-epichlorohydrin adduct containing quaternary ammonium groups canbe applied on the same ply or on two subsequent plies or between twoplies. Note that when the compound containing the sulfonic units isapplied to one ply and the amine polymer-epichlorohydrin adductcontaining quaternary ammonium groups applied to the subsequent ply, theprecipitate that is formed between the plies performs well as awater-resistant adhesive.

In the second method, the precipitate is formed first by mixing an aminepolymer-epichlorohydrin adduct containing at least one quaternaryammonium group and a water-soluble strengthening agent containing atleast one nucleophilic sulfonic unit and then it is applied to asubstrate. Similarly to the in-situ method, this method can be used fora single substrate as well as for a laminate structure of plies ofsubstrates. In the latter case, the precipitate can be applied to asingle ply or between two plies. Note that when the precipitate isapplied between two plies, it also performs well as a water-resistantadhesive.

Lignosulfonate may be used in either solid form (e.g. powder) or liquidform (e.g. solution or dispersion in water, or mixtures of water andorganic solvents). For example, lignosulfonate powder (e.g. LIGNOSITE100 from Georgia-Pacific Inc.) can be mixed with an aqueous KYMENE®solution and result in a precipitate, similar to the precipitateresulting from the mixture of lignosulfonate and KYMENE® solutions.Similarly, the KYMENE® can be used either in the solid form (e.g.powder) or liquid form (e.g. solution or dispersion in water, ormixtures of water and organic solvents).

In general, the solvent or dispersant of the solution or dispersion ofthe strengthening agents may or may not contain water, i.e., it can betotally aqueous, or totally organic, or it can contain mixtures of waterand organic solvents. Furthermore, the strengthening agents can be inpure form or in mixtures with other inert or active agents.

The reduction of bleeding of lignosulfonate from lignosulfonate-KYMENE®treated paper is shown in the following example.

EXAMPLE

The reduction of bleeding is checked by submerging paper samples inwater for a period of several days. Two sets of samples are prepared.The first set of samples is made using 35# linerboard (i.e., 35 poundsper thousand square feet; 35 lb/msf; 170 g/m² or 170 grams per squaremeter; product USP70 from Georgia-Pacific Inc.) dipped into an aqueoussolution of calcium lignosulfonate LIGNOSITE 50 for 1 minute. The secondset of samples is made using 35# linerboard dipped first into an aqueoussolution of calcium lignosulfonate for 1 minute, then wiped free ofexcess aqueous solution, and then dipped into an aqueous solution of5.0% KYMENE® 450 at pH=3 for 10 seconds. Both sets of samples are driedbetween two heated platens at 177° C. for 10 seconds. Both sets ofsamples are then submerged in water at room temperature for a period ofat least three days. The water around the lignosulfonate-treated samplesturns dark brown indicating that amounts of lignosulfonate bleed fromthe samples. However, the water around the lignosulfonate-KYMENE®treated samples remains clear indicating that no lignosulfonate bleedsfrom the samples.

We claim:
 1. A method of reducing the bleeding of lignosulfonate from asubstrate when contacted under humid conditions, said method comprisingthe steps of: a) applying a lignosulfonate to the substrate; and b)applying an amine polymer-epichlorohydrin adduct containing at least onequaternary ammonium group under acidic conditions to the substratehaving said lignosulfonate.
 2. A method according to claim 1, whereinsaid lignosulfonate is selected from the group consisting of metal saltsof lignosulfonic acid, ammonium salts of lignosulfonic acid, and anyfurther chemically modified lignosulfonic acid compounds wherein thenucleophilic sulfonic unit is preserved, and mixtures thereof.